The most commonly used display mode of the liquid crystal panel includes twisted nematic (TN) mode, vertical alignment (VA) mode and in plain switching (IPS) mode.
Using VA mode as an example: VA display is a normally black mode of vertically aligned and its polarization axis of the upper polarizing plate and the lower polarizing plate is vertical polarizer attachment. The principle of the VA liquid crystal display is based on the characteristic of the light transmittance changed with the size of the applied voltage. After the light through the polarizing plate of the lower substrate (i.e. TFT substrate), the light become linearly polarized light, the direction of the polarization is the direction of the polarization axis of the lower polarizing plate. When no voltage is applied, the light through the liquid crystal will not change the direction of the polarization, and the light will be received through the polarizing plate of the upper substrate (i.e. CF substrate), so that will be a dark state. After applying the voltage, the liquid crystal is deflected alone the alignment direction in the electric field. When the light is through the liquid crystal layer, the linearly polarized light is divided into two beams due to the refraction of the liquid crystal. Also, because of the two different beams of the propagation velocity, after synthesize the two beams, is bound to change the polarization direction of the polarized light. When the incident light reaches the polarizing plate of the upper substrate, the light parallel to the polarization axis direction of the lower polarizing plate can pass through, thus being a bright state. In the whole process of display, the liquid crystal has played the role of the light valve controlled by the voltage. This shows that the liquid crystal deflection capability of the polarization direction of the linearly polarized light is very important, it directly affects the result of the penetration.
The liquid crystal efficiency of the liquid crystal layer to the incident light is defined as: the polarized light generated by through the lower polarizing plate and parallel the direction of the polarization axis of the lower polarizing plate, in the maximum gray, exclude the absorb factors of the liquid crystal material, and after through the liquid crystal layer, what percentage of the direction of the polarization of the incident light can be deflected 90 degrees by the liquid crystal layer to penetrate out the light. In the prior art, the conventional method for measuring the liquid crystal efficiency is: measuring the transmittance of the liquid crystal panel many times, and excluding other factors of affecting transmittance by calculating, then calculated the liquid efficiency. However, the measurement of this method is more often, the variation in the measurement process is more, and made the approximations, the efficiency and accuracy are low.